With continuous advancement in the technology of semiconductor integrated circuits and continuous improvements in the performance of a semiconductor device, semiconductor devices also exhibit a trend of miniaturization. For example, a MIM capacitor within the device is an important component in an integrated circuit and has wide range of applications.
Among capacitors in the existing integrated circuits, the MIM capacitor has gradually become popular in radio frequency (RF) integrated circuits. A dielectric thin film deposited in MIM is mostly formed by PECVD (Plasma Enhanced Chemical Vapor Deposition), which is widely applied in fabricating a high-k silicon nitride thin film due to its low deposition temperature. In PECVD, the reaction gases comprising the precursor for Si element and the precursor for N element are usually ionized by means of microwave, RF or the like, and a high frequency power is introduced under certain temperature and pressure for inducing glow discharge to form plasma, so that a desired type of thin film is deposited on a wafer or substrate. Since the activity of plasma is used to promote the reaction, this kind of CVD (Chemical Vapor Deposition) is referred as PECVD.
The nature of a silicon nitride thin film directly determines the performance of a MIM capacitor, which thus poses relatively high requirements on the properties of the silicon nitride thin film. The wet etching rate of a thin film represents homogeneity of the deposited thin film. From the aspect of uniformity in the wet etching rate of thin films in the prior art, the high-k silicon nitride thin film prepared by PECVD has poor uniformity in the thin film. Therefore, it becomes difficult to further improve uniformity in the thin film based on the existing equipments.
In view of the above problems, the present invention is based on the insight that the thin film within the MIM device should have a better uniformity during deposition, in order to avoid different regions of the same thin film suffering from too large differences in etching rate, during the subsequent etching process of the thin film, due to uniformity in thickness of the thin film, i.e., to improve uniformity in the wet etching rate, and to increase capacitance uniformity of the resulting thin film within the MIM device. In addition the method of the present invention also removes some chemical defects during deposition of the thin film.